Extrinsic sensor

Claus, R. O. Gunther, M. F. Wang, A. Murphy, K. A., Extrinsic Fabry Perot sensor for strain and crack opening displacement measurements for 200 to 900° C, J. Smart Mater. Struct 1992, 1, 237 242... 

Extrinsic detectors, 22 180 Extrinsic fiber-optic sensors, 11 148 Extrinsic photoconductors, 19 138 Extrinsic semiconductors, 22 236-237 Extrinsic wastes, 10 68 Extruded food packaging, 18 45 Extruded lead-copper alloys, 14 776 Extruded lead-tellurium alloys, 14 778 Extruded rigid foam, 23 404-405 Extruders... 

The fiber optic sensors utilize an extrinsic Fabry-Perot interferometer to spectrally modulate light in proportion to pressure, temperature, or refractive index variations. Because they are based on spectral modulation instead of amplitude modulation, they are not affected by such common problems as fiber bending, connector losses, and aging. 

Fig. 9 Four waveguide-based sensors. Left Extrinsic sensors a in direct analyte measurements or c in indirect measurements by means of indicators or other reagents immobilized in membranes. Right Intrinsic sensors for measurements of changes in the light guided though the waveguide by b the adsorption of the analyte into its surface or by d the interaction of the analyte with a recognition phase, which is in direct contact with the waveguide...

In terms of the interaction of light with matter, extrinsic sensors can be compared with non-guided radiation sensors because light temporally exits the... 

Note. The Debye length (LD), although not introduced into the present simplified discussion, is a parameter frequently referred to in the gas-sensor literature. It was originally introduced into ionic solution theory and later applied to semiconductor theory where it is especially applicable to semi con -ductor/metal and semiconductor/semiconductor junctions. It is a measure of the distance beyond which the disturbance at the junction has effectively no influence on the electron distribution and therefore closely related to d (see Eq. (4.49)). It is a material parameter given by LD = (j kl /e2(, )12 where cQ is the undisturbed electron concentration, essentially the extrinsic electron concentration in the case of doped n-type tin oxide, and the other symbols have their usual meaning.)... 

Optical biosensors based on the use of fiber optics can be classified into two categories intrinsic sensors where interaction with the analyte occurs within an element of the optical fiber, and extrinsic sensors in which the optical fiber is used to couple light, usually to and fi om the region where the light beam is influenced by the measurand. Moreover, biosensors become attractive because they can be easily used by non-specialist personnel and they allow accurate determination with either none or little sample treatment. Therefore, fiber-optic biosensors may be especially useful in... 

Fig. 5.4. Optical Fiber biosensor, (a) Extrinsic optical fiber is used for the guiding the light to and from the sensor area, (b) Intrinsic the receptor molecules are immobilized on the fiber core after decladding of the fiber. The detection is based on fluorescence labels.

Fig. 3 Schematic diagram of an extrinsic-type sensor (optode)...

Both extrinsic- and intrinsic-type sensors incorporate a transducer element making it an active device. Extrinsic sensors have an external transducer, and the optical fiber just serves the purpose of a light carrier to and from the external transducer whereas, intrinsic sensors have the structure of the optical fiber modified to incorporate the transducer element. In both cases, the transduction mechanisms change the light properties based on interaction with chemical species. 

It was mentioned before that fiber-optic chemical and biosensors are broadly classified into two categories extrinsic- and intrinsic-type sensors. In the extrinsic-type sensors, the fiber is acting as a link connecting optical signals to (and from) the active material (medium) positioned at the end of the fiber, such as the Optode case. In the intrinsic-type sensors, the fiber is modified in different ways, through construction of the sensing component, which will be explained next. 

Recent work has investigated conductive polymers [69,70], sol-gels [71], and chemoresponsive dyes [72] for use as the gas-sensitive transduction medium in fiber optic sensors. In general, fiber optic sensors can be divided into two different sensing architectures extrinsic and intrinsic. If the transduction of the chemical signal into an optical signal occurs within the fiber... 

Fig. 5.6. (a) Extrinsic optical fiber sensor, where fibers are used to guide input and output signals, (b) Intrinsic optical fiber sensor, where sensor is incorporated into fiber structure... 

Due to their high sensitivity to strain, temperature variation, vibration, and acoustic waves, embedded extrinsic Fabry-Perot interferometric optical fiber sensors have been developed to detect delamination, based on changes in the acoustic properties of the materials before and after delamination [41]. Impact events and corrosion cracking generate ultrasonic waves, which can be characterized using elliptical core fiber sensors [40]. The in-line Fabry-Perot interferometer seems well suited for the local detection of shear waves and the characterization of impact-induced damage. 

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